Deforestation is cited as a cause of global warming and the reduction of carbon-dioxide emissions is the focus of attention as a global environmental problem. Forest resources are utilized in contemporary industries in the forms of wood, pulp, and paper. Various methods are being studied to reduce the amount of deforestation in order to prevent global warming. In the field of paper, efforts are being made worldwide to increase the rate of waste paper recycling.
Waste paper deinking is largely established as a method of waste paper recycling. In current methods, alkalis such as sodium hydroxide and sodium silicate, oxidative bleaching agents such as hydrogen peroxide, chelating agents, and agents such as surfactants are added to the waste paper to accelerate the release of ink from the pulp fiber. Thereafter, a washing technique and/or flotation technique is used to carry out deinking to separate the pulp and ink.
However, due to the variety of raw materials used in waste paper and the variety of printing techniques, deinking by the conventional deinking techniques is becoming problematic. Further, in order to solve problems concerning adhesion of foreign matter (stickies), fiber damage, effluent load and the like, neutral deinking is attracting attention as a deinking method that is kinder to the environment. In order to carry out neutral deinking more effectively, enzymatic treatments utilizing cellulase and the like are being studied.
A number of proposals have been put forth concerning deinking methods for waste paper using cellulase derived from fungi or bacteria. Kao Corp. proposes a deinking agent containing cellulase in JP Patent Publication (Unexamined Application) No. 59-9299, however there is no disclosure therein regarding the putative lowering of paper strength due to the action of the cellulase. In JP Patent Publication (Examined Application) No. 3-57235, Honshu Paper Co., Ltd. proposes a deinking technique for waste paper in which enzymatic treatment using alkali-resistant cellulase is performed at the same time as treatment with an alkaline deinking agent or after treatment with the deinking agent. In Japanese Patent No. 2805313, Oji Paper Co., Ltd. discloses a deinking technique in which treatment is conducted with a deinking agent after enzymatic treatment that contains cellulase. Further, in Japanese Patent No. 3042718, Novo Nordisk A/S attempts to find an enzyme component that can perform effective deinking by producing monocomponent cellulase. However, none of the above methods succeeded in providing an effective means for selecting an enzyme that realizes, at a low cost, a deinking effect that reduces the amount of the chemical agents that constitute an environmental burden or lower the strength (intensity) of waste paper in deinking.
Although various studies are being conducted, the rate of diffusion of enzymatic deinking is extremely low. Up to now, studies have been conducted on the application of cellulases to areas such as elimination of vessel pick, improvement of paper machine runnability and drainage, and deinking of waste paper. However, because of the high cost of cellulases and the fact that the action and effects of cellulases is not clear, the current situation is that cellulase has not been offered for practical use in areas other than elimination of vessel pick. Furthermore, because cellulase is an enzyme that degrades cellulose fiber, it has been pointed out that a decrease in the yield and the strength (intensity) of waste paper pulp after deinking is prone to occur.
Meanwhile, in deinking of waste paper, because the objects of effective deinking involve detachment and saponification of printing ink and pulp swelling, alkaline chemical agents and the like are used that amount to as much as several percent of the dry pulp weight. Further, as pulp is normally treated by being suspended in water of a volume that is equivalent to several dozen times the weight of the dry pulp, a vast amount of alkaline effluent is generated. Thus, because chemical agents are used in the treatment to neutralize the effluent, the recovery treatment is one that involves a heavy environmental burden. There is a need for development of an environmentally friendly deinking method that improves the current deinking technology that creates a heavy environmental burden.
Waste paper recycling is technology that indirectly protects forest resources and contributes to conservation of the global environment. It is anticipated that by further improvements such as reducing the environmental burden caused by waste effluent and decreasing the usage amount of chemical agents, the environmental adaptability of waste paper recycling will be enhanced. Thus, it was expected that enzymatic deinking would be applied as a technique to effectively remove ink at a neutral pH. However, its application has been postponed due to problems concerning decreases in the strength (intensity) of waste paper pulp and the cost of enzymes. Accordingly, the object of the present invention is to provide a cellulase deinking method for waste paper without lowering paper strength, that is implemented using an economically feasible enzyme amount that reduces the amount of deinking agents.